Apparatus and method for augmenting human vision by means of adaptive polarization filter grids

ABSTRACT

Methods and apparatus are described herein related to a see through head mountable device (HMD) configured to reduce glare originating from polarized light. Each eyeglass of the HMD is associated with a grid comprising a plurality of dynamically configurable polarization filters placed in the path of the light. A polarization analyzer module analyzes the polarization characteristics of a field of view and performs an optimization calculation. The polarization analyzer controls the said grid via a controller module in such a way that the filter state of each grid element can be addressed separately. The grid of polarization filters causes the polarization characteristics of the incident light to be adapted in such a way as to reduce glare and/or to provide a user of the said head mountable device with an enhanced visual perception of the field of view. The user of the described head mountable device has the option of selection between a plurality of polarization enhancement modes, such as horizontal or vertical polarization filtering only or a hybrid mode combining both horizontal and vertical polarization filtering on an individual basis for each grid element.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable to this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable to this application.

FIELD OF THE INVENTION

The present invention relates to augmented vision technology, and moreparticularly to a see through head mountable device making use ofadaptive polarization filter grids in order to optimize glare reduction.

BACKGROUND OF THE INVENTION Prior Art

Any discussion of the related art throughout the specification should inno way be considered as an admission that such related art is widelyknown or forms part of common general knowledge in the field. Unlessotherwise indicated herein, the materials described in this section arenot prior art to the claims in this application and are not admitted tobe prior art by inclusion in this section.

Polarized sunglasses have been known since the 1940s, when they werefirst invented as a means to reduce undesirable glare caused by sunlightbouncing off various surfaces in the field of view. Since those earlytimes polarized sunglasses have enjoyed massive popularity on theconsumer market. Continuous improvements have been made tosunglasses-related technology ever since. For example, materials havebeen developed that have different transmission characteristics overdifferent areas in the field of view. Also eyeglasses have been designedthat have different polarizations filters arrangements on an eyeglass, aconcept similar to bifocal eyeglasses. Moreover, electronic means existto selectively block out the glare of the sun by making a portion of theeyeglasses dynamically opaque by controlling liquid crystal multi-cellshutters. It is a recognized problem that polarized sunglasses do notwork well with polarized display screens because at particular viewingangles the display turns black. Methods have since been developed thatadapt such display devices so that they can be better viewed by userswearing polarized sunglasses. With the advent of see-through headmountable devices designed for augmented reality applications, wearablecomputer systems have recently reached a level of maturity whereby theyhave become suitable for performing very processor-intense real-timeimage processing tasks.

U.S. Pat. No. 4,848,890 issued on Jul. 18, 1989 to Michael Horndiscloses a novel visor with point sun blocking.

U.S. Pat. No. 7,506,976 issued on Mar. 24, 2009 to Baiocchi et. al.relates to a polarized transparent element wherein different portions ofthe glass are having a different luminous transmittance.

U.S. Pat. No. 7,683,983 issued on Mar. 23, 2010 to Zhong et al. relatesto a liquid crystal display that emits circularly-polarized light andthereby reduces perceived distortion when the display is viewed throughlinearly-polarizing filters such as polarized sunglasses.

U.S. Pat. No. 8,172,393 issued on May 8, 2012 to R. Tendler relates topolarized eyeglasses and more particularly to a method and apparatus forviewing instrumentation that has a polarized display.

US patent application 2014/0101608 teaches a general purpose userinterface for see through augmented reality type head mountable devices.

US patent application 2004/46927 teaches a new category of bifocalsunglasses utilizing a vertically polarized upper lens portion and anon-polarized light absorbing lower lens segment mechanically affixed tothe upper portion.

SUMMARY

The present invention recognizes that it is desirable to dynamicallyadapt the polarization characteristics of eyewear according toenvironmental factors. In other words the eyewear should be able toadapt itself to the scene being viewed by its wearer. Such adaptation isgenerally not possible without using electronic image processing means.Before the advent of augmented reality type head mountable devices therewere only limited means available to achieve that goal. The known priorart is generally restricted to methods of turning a part of the eyeglassopaque, so as to block out the glare of the sun and leave all otherparts of the eyeglass transparent.

The present invention solves the problem of eliminating glareoriginating from specular reflections by making use of a grid ofelectrically configurable polarization filters incorporated into theeyeglasses. Electrically configurable polarization filters are taught inthe prior art as a combination of a stack of voltage-controlledpolarization rotators followed by an anisotropic absorber. The presentinventor has realized that it is advantageous to miniaturize suchpolarization filters in such a way that a plurality of the saidpolarization filters is arranged as a grid, wherein each grid elementcan be controlled independently of the other grid elements. Each gridelement is intended to be small enough as to be no longer individuallydiscernible by the naked eye and is therefore also similar in characterto a pixel in a conventional spatial light modulator. A novelpolarization optimizing controller is furthermore disclosed. Variousembodiments of the invention are disclosed which enable the reduction ofglare from reflections off both horizontal and vertical surfaces at thesame time. Other embodiments can also work with additional filter anglesother than merely horizontal and vertical. Therefore glare can beeliminated or substantially reduced at any angle of reflection.Moreover, embodiments are introduced which enable the viewing ofpolarized display screens without the display appearing black at anyviewing angle, whilst at the same time eliminating glare from specularreflections. The present invention also introduces a novel type ofsee-through head mountable device which incorporates dynamic andreal-time optimization of polarization filtering.

This disclosure also details various embodiments of a suitable userinterface for the described polarization optimizer, relating to thepreferred embodiment in the form of a see through head mountableaugmented reality type device.

There has thus been outlined, rather broadly, some of the features ofthe disclosed polarization optimizer technique in order that thedetailed description thereof may be better understood, and in order thatthe present contribution to the art may be better appreciated. There areadditional features of the polarization optimizer technique that will bedescribed hereinafter and that will form the subject matter of theclaims appended hereto. In this respect, before explaining at least oneembodiment of the polarization optimization technique in detail, it isto be understood that the polarization optimization technique is notlimited in its application to the details of construction or to thearrangements of the components set forth in the following description orillustrated in the drawings. The polarization optimization technique iscapable of other embodiments and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein are for the purpose of the description andshould not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will become more fully understood from the detaileddescription given herein below and the accompanying drawings, whereinlike elements are represented by like reference characters, which aregiven by way of illustration only and thus are not limitative of theexample embodiments herein.

FIG. 1 illustrates a wearable computing system comprising polarizationoptimization, according to an example embodiment.

FIG. 2 shows a user interface scenario related to setting polarizermodes, according to an example embodiment.

FIG. 3 is a schematic diagram illustrating a polarization rotator,according to an example embodiment.

FIG. 4A is a schematic diagram illustrating an electrically controllablepolarization filter comprising polarizing film as an anisotropicabsorber, according to an example embodiment.

FIG. 4B is a schematic diagram illustrating an electrically controllablepolarization filter comprising a guest-host type liquid crystal cell asan anisotropic absorber with an added functionality of dynamicluminosity control, according to an example embodiment.

FIG. 4C is a schematic diagram illustrating the construction andfunction of a guest-host type liquid crystal cell, according to anexample embodiment.

FIG. 5 is a schematic diagram illustrating the overall architecture ofan example embodiment featuring an adaptive grid of polarizationfilters.

FIG. 6 is a flow chart illustrating a method for determining a preferredpolarization filter state, according to an example embodiment.

FIG. 7 is a schematic diagram illustrating different filter statescorresponding to various polarizer modes, according to an exampleembodiment.

FIG. 8 is a schematic diagram illustrating a method for optimizingpolarization filtering including polarized display detection, accordingto an example embodiment.

FIG. 9 is a schematic diagram illustrating the various polarizer modeswhich are selectable according to an example embodiment.

FIG. 10 is a block diagram illustrating the system architecture of anexample embodiment.

DETAILED DESCRIPTION A. Overview

In order to be able to build an embodiment of the present invention anumber of complex technological challenges have to be addressed. Mostsignificantly it is necessary to be able to construct a transparentpixel-type grid of miniaturized and electrically controllablepolarization filters. These polarization filters require suitablepolarization rotators as a key component. Also a polarization analyzeris specified which is capable of analyzing the polarizationcharacteristics of a real-world scene and to subsequently translate theanalysis into command inputs for a controller module of the said gridsin order to provide a user of one of the described embodiments with apolarization enhanced view of a real world field of view.

B. Example Polarization Rotators

FIG. 3 depicts a twisted nematic liquid crystal cell 300 which consistsessentially of a liquid crystal layer 301 placed between two treatedglass substrates 305. The inner-surfaces of the cell 300 are composed oftwo layers 306 and 307. The first layer 306 is a transparent electrodecomprising silver nano (AgNW) wires in the preferred embodiment butindium tin oxide, fluorine doped tin oxide and doped zinc oxide would beexamples of other materials constituting viable alternatives. The mainadvantage of utilizing silver nanowire technology in the preferredembodiment is that silver nanowire films allow excellent transmittanceand conductance and are therefore a preferred material for a transparentand flexible electrode in comparison to the brittle indium tin oxidetraditionally used in transparent electrodes. An embodiment of thepresent invention requires optimal transmittance characteristics fromthe transparent electrodes. The transparent electrodes used for thevarious embodiments should also exhibit only a minimum of in-planeoptical anisotropy, thus the absorption characteristics of suchelectrodes need to be as isotropic as possible in order to ensure thatlight of all polarization angles is absorbed equally, at least until thepoint where it has been directed through the stack of polarizationrotators and through an anisotropic absorber at the end of each stack(or alternatively a single absorber in the optical path following theplurality of stacks). Other than silver nanowire and the traditionalindium tin oxide, other transparent conducting oxides may also serve therequirements placed on the transparent electrode. Moreover, organicmaterials such as carbon nanotube networks and graphene may also be usedas potential alternatives. The transparent electrode layer 306 permitsthe application of an electrical field 311 across the cell as well asswitching the cell between the OFF state 300 and the ON state 390. Thesecond layer 307 is responsible for the homogenous alignment of theliquid crystal. In the preferred embodiment of the present invention itcomprises a rubbed polyimide layer of about 100 nm.

The liquid crystal alignment at both sides of the cell is defined duringcell manufacturing. By careful control any twist-angle can be induced inthe helical structure across the liquid crystal layer. With atwist-angle of exactly 90 degrees, the standard 90 degree twistednematic cell is formed. Twist-angles of less than 90 degrees form thelow-twist cell whereas by definition, super-twist cells are cells thatpossess twist-angles exceeding 180 degrees. The preferred embodiment ofthe present invention uses a standard cell comprising a 90 degree twist.

The two glass 305 substrates are separated by spacers of usually between3 mm and 20 mm and are typically sealed with glue. When the polarizationrotator is in the OFF state 300, the helical structure formed by theliquid crystal molecules rotates the entrance polarization. In the ONstate 390 the polarization rotary power is suspended and thepolarization state of the light entering normally to the entrancesurface 180 is not altered by the twisted nematic cell. In FIG. 3 alight source 135 produces incident light 180 of a vertical polarizationstate 385, whereby on passing through the twisted nematic cell 300 inthe OFF state the exiting light 181 is changed to a state of horizontalpolarization 386 before reaching a human eye 183. Correspondingly in theON state 301 of the twisted nematic cell the vertical polarization state385 of the incident light 385 remains unchanged in the exiting light181.

A 100 percent efficient rotation of a linear entrance polarization canonly be obtained in the limit of large cell thickness and in general theexiting light 181 becomes elliptically polarized with componentsoscillating in directions lying both parallel and perpendicular to theexit liquid crystal molecules. Furthermore, it is the optical pathdifference in the liquid crystal cell that affects the overall magnitudeof the polarization efficiency for the twisted nematic cell.

In exemplary implementations, the transmitted intensity I that passesthrough a polarization rotator is modeled by Malus' law (Eq. 1):I=I ₀ sin²(θ)  (Eq. 1)

where I₀ is the intensity after passing through the polarization rotatorand θ is angle of polarization after passing through the liquid crystallayer. This model only strictly applies for rays of incident lightoriented perpendicular to the plane of the transparent electrode of thepolarization rotator cell. At oblique angles birefringence of the liquidcrystal produces elliptical, rather than linear, polarization states.However, this model is a close approximation for the viewing anglesconsidered in the proof-of-concept embodiment. For the proof-of-conceptembodiment a nematic liquid crystal mixture (supplied by Chisso,birefringence Δn=0.137) with chiral dopant was sandwiched between 50 nmthick rubbed polyimide alignment films (AL-1254 supplied by JapanSynthetic Rubber) on indium tin oxide electrodes of transparent glasssubstrates. The rubbing directions of the two alignment films werecrossed at 45 degrees or 90 degrees. The thickness d and Δn of thetwisted nematic liquid crystal cells are needed to satisfy the followingrelation, called the Mauguin limit to obtain sufficient polarizationrotatory power for incident light of wavelength λλnd>2λ  (Eq. 2)

According to the above equation (Eq. 2) for white light of visible lightwavelength, the thickness d was determined at 10 μm, and was suspendedusing spherical plastic spacers dispersed uniformly in the twistednematic liquid crystal cells.

C. Example Electrically-Controllable Liquid Crystal Polarizing Filters

FIG. 4 shows an example embodiment of electrically-controllablepolarizing filters using two different twisted nematic liquid crystalcells as a polarization rotator. It is composed of 45 degree (404) and90 degree (406) twisted nematic liquid crystal cells and a fixedpolarizing film 408. The light with arbitrary polarization plane atangle θ to the optical transmitting axis of the polarizing film 402 isincident to the 45 degree twisted nematic liquid crystal cell 404. The45 degree and 90 degree twisted nematic liquid crystal cells are piledup so that the alignment directors of liquid crystal molecules in thesetwo cells are twisted continuously along the optical path through thetwisted nematic liquid crystal cells without any external voltage. Theliquid crystal director on the output side of the 90 degree twistednematic liquid crystal is parallel to the transmitting axis of thepolarizing film. When the twisted nematic liquid crystal cells aredriven independently by an external voltage applied to transparentelectrodes of silver nanowire or indium tin oxide, the polarizing filteroperates as follows: the two twisted nematic liquid crystal cellswithout applied voltage rotate the polarization plane oflinearly-polarized incident light through 45 degrees and 90 degrees,according to the optical rotatory power known as the twisted nematiceffect. This phenomenon is caused by the difference between therefractive indices for right circularly and left circularly polarizedlight components of the linearly-polarized incident light based on thehelical liquid crystal alignment structure. As the liquid crystaldirectors in the two twisted nematic liquid crystal cells are twistedcontinuously through the two cells, the polarization rotatory powers inthe two twisted nematic liquid crystal cells are added. The incidentpolarization plane is therefore rotated through 135 degrees. Otherwise,when sufficient voltage is applied through circuits 405 and 410 to bothtwisted nematic liquid crystal cells, the liquid crystal molecules inthe two twisted nematic liquid crystal cells are realigned parallel tothe applied electric field. The twisted alignment of liquid crystalmolecules in the twisted nematic liquid crystal cells is unwound, so theincident polarization plane is not rotated by these cells.

When the polarization rotatory power of either twisted nematic liquidcrystal cell disappears under sufficient applied voltage, the serialcombination of the two twisted nematic liquid crystal cells can rotatethe incident polarization plane through 45 degrees or 90 degrees.Consequently, by controlling the voltages applied to the twisted nematicliquid crystal cells, using electrical switches 405 and 410 shown inFIG. 4A, the polarization plane of incident light 400 is rotated through0 degrees, 45 degrees, 90 degrees or 135 degrees, depending on thecombination of the on/off-states of 405 and 410. The unwanted reflectedlight is absorbed by the fixed polarizing film 408, after itspolarization plane is rotated to the optimum angle at a 45 degreesinterval.

The fabricated 45 degrees and 90 degrees twisted nematic liquid crystalcells are piled up compactly with a polarizing film (supplied by Luceo),which has comparatively small dependence of light transmittance on thevisible wavelength. The total transmittance of the filter forunpolarized white light is approximately 30 percent. The lighttransmittance can be increased by reducing light reflection at thesurfaces of the twisted nematic cells and the polarizing film. Thisimprovement is achieved in a preferred embodiment by depositinganti-reflection dielectric thin films on the cell surfaces, and it alsoprevents a flare effect of the object image when strong light isincident to the polarizing filter.

Instead of the polarizing film 408, a guest-host type of homogeneousnematic liquid crystal cell containing black dichroic dye may be used asthe anisotropic absorber in an alternative embodiment. A schematicdiagram of that embodiment is illustrated in FIG. 4B. In that embodimentthe light absorbance as well as the polarization angle can becontrolled. This is because light absorption of the guest-host typeliquid crystal cell for polarized light varies significantly with theexternal voltage 452 applied to transparent electrodes of the guest-hosttype liquid crystal cell 450. Those skilled in the art will realize thatother than polarizing film or guest-host type liquid crystal cells anyother anisotropic absorber of polarized light can be used in alternativeembodiments.

The transmitted light from the polarizing filter becomes minimum whenthe incident polarization angle is 90 degrees because the twistednematic liquid crystal cells do not rotate the incident polarizationplane in a state wherein the twisted nematic liquid crystal cells aredriven by the applied voltage. When removing the applied voltage fromone or both of the twisted nematic liquid crystal cells, thepolarization angle for minimum transmittance is shifted from 90 degrees.The deviation angles correspond to the polarization rotation angles inthe two twisted nematic liquid crystal cells. Since the polarizingfilter of the described embodiment selectively suppresses incident lightwith polarization angles of 0 degrees, 45 degrees, 90 degrees and 135degrees, more than 80 percent of polarized light for arbitrarypolarization angles other than 0 degrees, 45 degrees, 90 degrees and 135degrees can be eliminated by changing the combination of on/off statesof switches 405 and 410. Those skilled in the art will appreciate thateven though the preferred embodiment of the present invention comprisesfour pre-set polarization angles for the polarizing filter, otherconfigurations are also possible. In particular an embodiment of theinvention is configured only for polarization angles 0 degrees and 90degrees comprising only a single polarization rotator.

D. Example Polarization Filter Grid Controllers

The present invention makes uses of a plurality of polarization filtergrids 110 and 112 in order to present a user of a head-mountable devicewith a view of their surroundings which is optimized in terms ofpolarization filtering. It has already been specified in the previoussections how an individual grid element of the said polarization filtergrid may be implemented in various embodiments. This section specifieshow the grid itself is controlled in the sense of how variousembodiments may determine the target polarization filter state for eachgrid element. FIG. 5 shows an example embodiment wherein for simplicityonly vertical and horizontal polarization states are processed,therefore in that embodiment the grid elements of the polarizationfilter are only set to either horizontal or vertical polarization.However those skilled in the art will appreciate that the invention canbe practiced with an arbitrary number of polarization states. Thepreferred embodiment has 4 polarization filter states for each gridelement, namely 0 degrees, 45 degrees, 90 degrees and 135 degrees. Inthe simple embodiment of FIG. 5 which is restricted to the filter statesof 0 degrees and 90 degrees, two separate image capture devices 141 and142 are utilized. The image capture devices take images of the field ofview of the user through polaroid filters 143 and 144, wherein filter143 is a vertically transmissive filter and filter 144 is a horizontallytransmissive filter. Those skilled in the art will appreciate that otherconfigurations are possible in order to capture the field of view withdifferent polarization filters, so that these images may be comparedwith each other in the following steps. Following is a subset of thepossible alternatives. It is possible to have a camera for each eye andfor each polaroid filter. The said constellation would thus comprisefour such cameras in total. The advantages of such constellation wouldbe that the required images could be captured in parallel, as opposed tosequentially, as would need to be the case in a single cameraembodiment. The advantage of having cameras corresponding to each eye,as opposed to mounting the cameras in a central position between theeyes is that it then becomes possible to adapt the polarization filtergrids for a particular eye, meaning that the filter grid for the lefteye would be controlled independently of the filter grid for the righteye. In this way, having separate cameras for each eye ensures thatparallax effects can be easily compensated for. The preferred embodimentuses a camera for the left eye coupled with a polaroid sheet ofhorizontal polarization in front of its lens and a camera for the righteye coupled with a polaroid sheet of vertical polarization in front ofits lens, however it is immaterial which eye camera is coupled withwhich polarization filter. What is important in the preferred embodimentis that the camera for each eye is coupled with a polaroid sheet ofopposite polarization as that for the other eye. It is not necessary touse polaroid sheets as polarization filters for the respective camera.An embodiment of the present invention uses only a single cameraprefixed with an electrically controlled twisted nematic polarizationfilter of a similar type as described in the preceding section. Theadvantage of using electrically controlled polarizations filters inconjunction with the polarization analyzer cameras is that morepolarization filter states can be analyzed without having to add aseparate camera/polaroid combination for each desired polarizationangle. An advantageous combination is to have a separate camera for eacheye and to prefix each of it with said electrically controlled twistednematic polarizing filter. The cameras then simultaneously captureimages in sequence of polarization state. So both the said left-eyecamera and right-eye camera would first capture an image each in a 0degree polarization filter setting, followed by images at 45 degree, 90degree, and 135 degree of polarization setting respectively. However,any other sequence of any polarization angle is also possible.

In the embodiment described in FIG. 5 the image capture process resultsin image 514, taken in combination with a vertical polaroid filter andimage 516, taken in combination with a horizontal polaroid filter. Theimages in the example have both captured the same real-world object 502,which is illuminated by an unpolarized light source 500. The real-worldobject 502 features a horizontal top surface. When unpolarized lightreflects off that top surface it becomes horizontally polarized. Thereflected light 504 and 512 is what causes undesirable glare. Filter 143is configured to only let through light of vertical polarization,therefore in image 514 the amount of glare coming off the top surface ofthe real-world object 502 is greatly reduced. On the other hand, image516 eliminates the glare coming of the right side of the real-worldobject 502. The said right side of the said object is a vertical surfaceand as such the light that reflects off that surface is substantially ofvertical polarization. As a result of filtering out such verticalpolarization with polaroid sheet 144 on image 516 the glare coming ofthe right side of the said object is greatly reduced. Both images 516and 516 are subsequently analyzed by the polarization analyzer component530. The images are processed as a matrix of picture elements or pixels.Each pixel of image 514 is then compared to each corresponding pixel ofimage 516. The comparison involves estimating which one of the comparedpixels comprises the least amount of glare. Once that pixel has beenidentified it also identifies the filter associated with the image thatthe pixel corresponds to. The polarization analyzer 530 populates apixel matrix comprising optimal polarization filter settings for eachpixel. Each element of the said matrix therefore contains information asto which of the available polarization filters produces the least amountof glare for the said pixel. The next step that the polarizationanalyzer 530 performs is a smoothing step. The present inventor hasfound out that for a good user experience it is essential thatnoticeable isolated and abrupt changes in polarization filtering need tobe avoided. An example would be a surface of a real-world object whichis represented by 100 pixels on the said polarization analyzer matrix.If, in the example, the polarization analyzer determines that 5 of thesepixels, randomly distributed, are at an optimum with a horizontalpolaroid filter and 95 of these pixels are at an optimum with a verticalpolaroid filter, then the smoothing step would set all 100 pixels to ahorizontal filter setting. Without the smoothing step the real-worldsurface would eventually be viewed by a user of the present invention ascontaining spots or blotches of a slightly different shade than the restof the surface. The smoothing step therefore aims to identify distinctzones of pixels for a particular filter setting. The smoothing step,however, becomes obsolete if the polarization filter matrix comprisesenough elements that an individual pixel can no longer be discerned bythe naked eye. The present inventor has estimated that the resolution ofthe pixel matrix, and by extension the associated filter grid, shouldideally be to be at least 640 by 480 before it becomes advisable toforego the smoothing step. In the example of FIG. 5 the polarizationanalyzer is able to determine that image area 518 benefits from avertical polaroid filter and that image area 520 benefits from ahorizontal polaroid filter. If there are any image areas that areindeterminate in terms of polarization optimization, then a defaultpolarizing filter setting is being applied to these areas. In apreferred embodiment the default polarization filter state is set toallow vertical transmission in analogy to traditional polarizedeyeglasses designed for sun protection. A preferred embodiment alsoconfigures the polarizing filter grid in such a way that when the deviceis not powered up all polarizing filters remain in the default setting,which means that they are set to allow transmission of verticallypolarized light. Once the polarization analyzer 530 has identifiedpreferred polarization filter settings for distinct image areas, thepolarization filter grid controller 532 is invoked as the next step. Thepurpose of the polarization filter grid controller 532 is to translatethe calculated polarization filter targets into control inputs for theplurality of individual polarization rotators 526 housed within thegrids of polarization filters 533. Hence area 518 which has beendetermined to benefit from a vertically transmissive polarization filteris mapped to the polarization filters demarcated by 522. The saidpolarization filters are subsequently set to become verticallytransmissive by the polarization filter grid controller 532.Correspondingly the polarization filters demarcated by 524 are set tohorizontally transmissive by the polarization filter grid controller532. The remaining polarization filters in the example belong to areasof indeterminate polarization optimum and are therefore set to thedefault polarization filter setting. As a result of the steps describedin the example the real-world object 502 appears to a human eye 183 in away that glare originating both from the horizontal and verticalreflections from the object surfaces is equally reduced in the image 528that the user 210 perceives.

The preferred embodiment comprises six distinct polarization modes,namely polarization unaltered 902, overall vertical polarization 908,overall horizontal polarization 910, optimized vertical polarization904, optimized horizontal polarization 906 and overall optimizedpolarization 912, as is depicted in FIG. 9. The preferred embodimentallows a user of a head mountable device 102 to switch between thevarious polarizer modes, via the polarization mode selector 920, byeither tapping the touchpad 124, by issuing a voice command 250 or by asmartphone app 227 (as depicted in FIG. 2). The “polarization unaltered”mode attempts to render real-worlds objects as they would be experiencedby a user wearing non-polarized sunglasses. The “overall verticalpolarization” mode simulates what a user would see if they woresunglasses equipped with a vertically transmissive polaroid filter.Consequently the “overall horizontal polarization” mode simulates what auser would see if they wore sunglasses equipped with a horizontallytransmissive polaroid filter. The “optimized vertical polarization” modeattempts to selectively suppress reflections off horizontal surfaces,whereas the “optimized horizontal polarization” mode attempts toselectively suppress reflections off vertical surfaces. The “overalloptimized” mode attempts to selectively suppress reflections both offhorizontal and vertical surfaces. The difference between the “optimized”and the “overall” modes is that in the “optimized” mode all image areaswhich are not subject to glare will appear as they would appear to aperson wearing non-polarized ordinary sunglasses. One major advantage ofthe “optimized” setting is that the user is able to view a liquidcrystal computer display, television screen or digital watch, forexample, without the screen appearing to become black when viewed atcertain angles. Therefore the “optimized” setting attempts to eliminatethe undesired side effects exhibited by sunglasses coated with polaroidfilm. Those skilled in the art will appreciate that the presentinvention may also be practiced with other polarizer modes and othercombinations of such.

FIG. 7 depicts how the various polarization modes of the preferredembodiment may be realized. The “polarization unaltered” 701 mode is aparticular challenge since the apparatus used for the preferredembodiment does not allow to bypass a polarizing filter cell. Thereforethe cell will always be transmissive to a particular polarization anglewhilst blocking all other angles. The present inventor has solved theproblem of implementing a “polarization unaltered” mode by configuringthe filter cells for alternate polarization states. Therefore each rowof the filter grid sets the grid elements to an alternate target state715. If, for example, the first filter cell is configured for verticaltransmission, then the next filter cell is set to horizontaltransmission, the next filter cell again to vertical transmission and soon. As long as the filter grid has a high enough resolution (ideallybetter than an grid of 800 by 600 filter cells), the user is no longerable to discern the alternating filter states and the user perceptionbecomes similar to the scene being viewed with non-polarized sunglasses.For the “overall vertical polarization” 705 state the individual cellsof the filter grid 717 are all configured to transmit light of the samepolarization angle of 90 degrees. For the “overall horizontalpolarization” state (not depicted) the same principle is used albeitwith a uniform polarization angle of 0 degrees. For the “optimizedvertical polarization” state, at first all cells are configured for thealternating polarization sequence depicted in 701 as “polarizationunaltered”. With the assistance of the polarization analyzer module 530reflections off horizontal surfaces are identified and eliminated byselectively setting the corresponding filter cells of the filter grid719 to vertical transmission mode 703. For the “optimized horizontalpolarization” mode (not depicted) the same method is used as for“optimized vertical polarization” with the exception that glarereflecting off vertical surfaces is by eliminated by setting distinctfilter cells to vertical transmission only. The “overall optimizedpolarization” mode 707 is a combination of the “optimized horizontalpolarization” mode and the “optimized vertical polarization” mode 703.Consequently glare reflecting off both vertical and horizontal surfacesis eliminated by setting distinct filter cells corresponding toidentified areas of glare to vertical or horizontal transmission only.All other cells are configured to work with alternating polarizationsettings. FIG. 6 depicts the steps taken by the polarization analyzer todetermine the preferred polarization filter setting for a given pixel.In the example embodiment of FIG. 6 the polarization analyzer takes asinput the image 514 taken with a horizontal polaroid filter and theimage 516 taken with a vertical polaroid filter. The polarizationanalyzer then normalizes the images and transposes them onto an imagematrix wherein each matrix element corresponds to a filter cell in thegrid of polarization filters. For each element of the image matrix(subsequently referred to as “pixel”) an sRGB value can be read for boththe horizontal filter setting 609 and the vertical filter 605 setting.The next step is the calculation of the respective CIE XYZ tristimulusvalues 607 612 from the sRGB tristimulus values in the form of a lineartransformation, which may be carried out by a matrix multiplication.Assuming that the Again the sRGB component values R_(srgb), G_(srgb),B_(srgb) are in the range 0 to 1, the following equation may be used tocalculate C_(linear) where C is R, G or B:

$\begin{matrix}{C_{linear} = \left\{ \begin{matrix}{\frac{C_{srgb}}{12.92},} & {C_{srgb} \leq 0.04045} \\{\left( \frac{C_{srgb} + a}{1 + a} \right)^{2.4},} & {C_{srgb} > 0.04045}\end{matrix} \right.} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

In the above equation (Eq. 3) a=0.055 and C is R, G or B.

The next step involves putting the resulting values through a matrixmultiplication of the linear values in order to get XYZ. The necessaryequation (Eq. 4) is specified as follows:

$\begin{matrix}{\left| \begin{matrix}X \\Y \\Z\end{matrix} \right| = \left| \begin{matrix}0.4124 & 0.3576 & 0.1805 \\0.2126 & 0.7152 & 0.0722 \\0.0193 & 0.1192 & 0.9505\end{matrix} \middle| \; \middle| \begin{matrix}R_{linear} \\G_{linear} \\B_{linear}\end{matrix} \right|} & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$

The CIE XYZ color space was deliberately designed so that the Yparameter was a measure of the brightness or luminance of a color. Thechromaticity of a color was then specified by the two derived parametersx and y, two of the three normalized values which are functions of allthree tristimulus values X, Y, and Z. By being able to estimate thelevel of brightness in this way the described example embodiment thenmakes use of the linear transformation to estimate whether thehorizontally transmissive filter or the vertically transmissive filterhas transmitted more specular light. When unpolarized light is hitting ahorizontal surface the specular light bounces off the surface, becomeshorizontally polarized and heads towards the camera. If it then hits thevertically transmissive polaroid filter it all gets absorbed by thefilter. If on the other hand it hits the horizontally transmissivepolaroid filter the specular light is passing through unhindered.Meanwhile, the diffuse light that gets absorbed and retransmitted by thesurface is unpolarized. Each of the polaroid sheets equally absorbs halfof that diffuse light, and the rest hits the camera. So the brightnessof a pixel on the polarizer grid always comprises 50 percent of thediffuse light and a variable amount of the specular light. Therefore itis possible to reliably estimate the best polarizing filter setting bycomparing the various levels of luminance of a polarizer grid pixel inrelation to the various polarizing filter settings. This is what isbeing achieved in step 614. For example, if the pixel luminance isgreater with a horizontally transmissive filter than with a verticallytransmissive filter, then the target setting for the correspondingfilter cell is set to vertical transmission. This corresponds to step620 of the flow chart. Step 616 is the equivalent for the alternativepolarization scenario, therefore if the pixel luminance is smaller witha horizontally transmissive filter than with a vertically transmissivefilter, then the target setting for the corresponding filter cell is setto horizontal transmission. A third scenario 618 is also possible, thisoccurs if there is no significant difference in relation to the comparedpixel-specific horizontal/vertical luminance values. In that case thepolarization target for the respective target pixel is set toindeterminate. By following the steps depicted in the flow chart of FIG.6 one can thus ensure that the largest possible amount of specular lightis blocked out. However, the present inventor has realized that onespecial exception also needs to be taken into account. If the user of ahead mountable device embodying the present invention were to look at adisplay screen emitting polarized light, such as a liquid crystalscreen, it is possible that the polarizing analyzer sees a pixel asblack in one filter setting and as bright white in another filtersetting. The algorithm described above would then erroneously take thedarker luminance as indicative of the correct polarization filtertarget. The screen would consequently appear black to the user, which isnot intended. To solve this problem the present inventor has created anembodiment wherein an additional operation is performed in thepolarization analyzer. The said embodiment is depicted in FIG. 8. Thefigure shows a real-word scene comprising a cuboid object 502 which hasareas of undesirable glare 805. The scene also comprises a liquidcrystal display 227. The scene is subsequently captured by a camera witha horizontally transmissive polaroid filter resulting in image 844 andby a camera with a vertically transmissive polaroid filter resulting inimage 842. Both images are processed by the polarization analyzer 530.When comparing pixels of images 844 and 842 the polarization analyzermakes use a special rule 801 in order to be able to differentiatebetween undesirable glare and a polarized display screen. Such a screenmay appear black with one polaroid filter and significantly brighterwith another polaroid filter. An area comprising glare, on the otherhand, will generally exhibit a lesser luminosity differential withdifferent filters. The polarization analyzer therefore identifies pixelsof peak luminance and measures the difference in luminance betweendifferent polaroid filters for that pixel. The peak luminance pixels areinterpreted to belong to areas of glare and the luminance differencesfor these pixels can serve as a benchmark for comparing them with pixelsrelated to a suspected display screen. This concept is illustrated inFIG. 8 with the help of example pixels A and B. In the verticallypolarized image 842 of the real-world scene 841 these two specificpixels are marked as pixel A(V) 810 and pixel B(V) 820. Correspondinglyin the horizontally polarized image 844 there are the equivalent pixelsA(H) 812 and B(H) 824. Pixel B is located in an image area associatedwith a liquid crystal display screen, whereas pixel A is not located inan image area associated with a liquid crystal display screen. In theexample, pixel A(H) exhibits more luminosity than pixel A(V), whereaspixel B(V) exhibits more luminosity than pixel A(V). After applyingspecial rule 801 for the polarization analyzer 530, the polarizationfilter grid controller 532 ensures that the image reaching the user'seye 183 is polarization-optimized in such a way that the real-worldglare on the cuboid object is reduced both on its horizontal andvertical surfaces, whilst at the same time ensuring that the liquidcrystal display, which is also part of the same real-world scene, doesnot appear blacked out. In another embodiment instead of comparing peakluminance levels for different filter states, the average luminancedifferential for different filter setting over a field of view can beused as a benchmark. A pixel is suspected to be related to a displayscreen if the pixel appears essentially black in one filter setting butnot in another filter setting, therefore the luminance differentialbetween different filter settings for pixels relating to a polarizeddisplay screen tends to be greater than the differential of said peakluminance. Another characteristic of a polarized display screen is thatthe luminance tends to be greater than that of surrounding objects dueto the backlighting employed in such screen devices. Therefore a pixelthat appears essentially black in one polarizing filter setting andbrighter than the average pixel brightness summed over the entire fieldof view is indicative of belonging to a polarized display screen.

In an alternative embodiment the polarization analyzer may also beconfigured to analyze the expected loss of brightness of lighttransmitted through each individual element of the said polarizationfilter grid. As a result of the said the analysis, the polarizationanalyzer module may not only optimize polarization filter states foreach filter grid element but it may also optimize the brightness of thelight transmitted through each filter element. An adjustment of thebrightness of the transmitted light may be implemented in the form of aspatial light modulator which allows amplitude modulation. Such aspatial light modulator can be placed anywhere in the optical path ofthe incident light. A spatial light modulator may also form an integralcomponent of stack of polarization rotators. In an embodiment the saidspatial light modulator is controlled by the polarization gridcontroller, which in turn is controlled by the polarization analyzer.Those skilled in the art will appreciate that the spatial lightmodulator may also normalize other properties of the incident light, sothat a user of an embodiment of the present invention may experience thefield of view free of pixilation effects. Such pixilation effects wouldoccur when for example when different polarization filter settings areassociated with different light absorption characteristics. Also,different filter states may be associated with differentwavelength-dependent absorbance characteristics. In the describedembodiment it is the task of the said spatial light modulator tonormalize such effects in order to avoid pixilation effects which arereadily noticeable by a user of the described device.

In another embodiment the adjustment of the brightness of thetransmitted light is achieved by using a guest-host type of homogeneousnematic liquid crystal (GH-LC) cell, as depicted in FIG. 4C, wherein theGH-LC cell comprises black dichroic dye 482 and wherein the polarizationanalyzer may, via the polarization grid controller, influence both thepolarization angle as well as the light absorption characteristics ofeach individual cell. This is because light absorption of the GH-LC cellfor polarized light varies significantly with the external voltage 471applied to the transparent electrodes of the GH-LC cell. In this way,without any applied voltage 491, the director of liquid crystal anddichroic dye molecules are uniformly aligned parallel to the indium tinoxide surfaces 474, and incident light with a polarization planeparallel to the alignment of the dye molecules is strongly absorbed.Otherwise, when applying a sufficient external voltage to the GH-LC cell492 the dichroic dye molecules 482 aligned with the liquid molecules 480are reoriented parallel to the applied electric field, and the lightabsorbance of the dye is decreased, as can be seen in the graph 493. Ingraph 493 the v-axis 470 depicts luminous transmittance, whereas thex-axis 472 depicts the applied voltage. The described embodiment usingGH-LC cells is utilizing a nematic liquid crystal mixture (JB-1000XXsupplied by Chisso) containing black dichroic dye which is sandwichedbetween polyimide alignment layers rubbed in parallel resulting in GH-LCcells of a thickness of 10 μm.

E. Example Head-Mountable Devices

Systems and devices in which example embodiments can be implemented willnow be described in greater detail. In general, an example system can beimplemented in or can take the form of a wearable computer (alsoreferred to as a wearable computing device). In an example embodiment, awearable computer takes the form of or includes a head-mountable device(HMD).

An example system can also be implemented in conjunction with otherinterconnected components, such as a mobile phone, among otherpossibilities. An example system can also take the form of a device suchas a wearable computer and a plurality of subsystems of such a device.

A head mountable device can generally be any device that is capable ofbeing worn on the head and places a spatial light modulator in front ofone or both eyes of the wearer. A head mountable device can take variousforms such as a helmet or eyeglasses. As such, references to“eyeglasses” or a “glasses-style” head mountable device should beunderstood to refer to a head mountable device that has a glasses-likeframe so that it can be worn on the head. Further, example embodimentscan be implemented by or in association with a head mountable devicewith no display, a single display or with two displays.

FIG. 1 illustrates a wearable computing system according to an exampleembodiment. In FIG. 1, the wearable computing system takes the form of ahead-mountable device (head mountable device) 102. It should beunderstood, however, that example systems and devices can take the formof or be implemented within or in association with other types ofdevices, without departing from the scope of the invention. Asillustrated in FIG. 1, the head mountable device 102 includes frameelements including lens-frames 104, 106 and a center frame support 108,lens elements 110, 112, and extending side-arms 114, 116. The centerframe support 108 and the extending side-arms 114, 116 are configured tosecure the head mountable device 102 to a user's face via a user's noseand ears, respectively.

Each of the frame elements 104, 106, and 108 and the extending side-arms114, 116 can be formed of a solid structure of plastic and/or metal, orcan be formed of a hollow structure of similar material so as to allowwiring and component interconnects to be internally routed through thehead mountable device 102. Other materials can be possible as well.

One or more of each of the lens elements 110, 112 can be formed of anymaterial that can suitably incorporate a grid of polarization filterstacks such as specified previously. Lens elements 110 and 112 eachcomprise one single grid, which in the diagram of FIG. 1 is symbolicallydepicted by the grid lines drawn on each lens element 110, 112. As canbe seen in FIG. 1, each of the grid elements comprises one singlepolarization filter stack. FIG. 4A and FIG. 4B subsequently go on todepict the intrinsic components which make up such a polarization filterstack. In the specific example shown in FIG. 1, polarization filterstack 125 is differentiated from polarization filter stack 126 in termsof polarization selection. In the diagram, the vertical bars drawn onstack 125 denote that stack 125 is momentarily set to filter vertically,whereas conversely the horizontal bars of stack 126 denote that thatfilter is momentarily set for horizontal polarization filtering. FIG. 1depicts a preferred embodiment, wherein any one of the stacks can bedynamically set at runtime to one of four possible distinct polarizationfilter states: 0 degree filtering 150, 45 degree filtering 151, 90degree filtering 152 and 135 degree filtering 153. So when a lightsource 135 produces rays 136 of unpolarized light, these rays maysubsequently reflect off a surface. If said surface is a verticalsurface, such as 131, then the reflected light ray becomes a verticallypolarized ray 138. If, on the other hand, said surface is a horizontalone, such as 132, then a reflected ray 137 will exhibit a horizontalpolarization state. The lens elements can additionally facilitate anaugmented reality or heads-up display where the projected image orgraphic is superimposed over a real-world view as perceived by the userthrough the lens elements.

The extending side-arms 114, 116 can each be projections that extendaway from the lens-frames 104, 106, respectively, and can be positionedbehind a user's ears to secure the head mountable device 102 to theuser. The extending side-arms 114, 116 can further secure the headmountable device 102 to the user by extending around a rear portion ofthe user's head. Additionally or alternatively, for example, the headmountable device 102 can connect to or be affixed within a head-mountedhelmet structure. Other configurations for a head mountable device arealso possible.

The head mountable device 102 can also include an on-board computingsystem 118, and a variety of optional utility devices, such as an imagecapture device or a finger-operable touch pad. The on-board computingsystem 118 is shown to be positioned on the extending side-arm 114 ofthe head mountable device 102; however, the on-board computing system118 can be provided on other parts of the head mountable device 102 orcan be remotely positioned from the head mountable device 102 (e.g. theon-board computing system 118 could be wire- or wirelessly-connected tothe head mountable device 102). The on-board computing system 118 caninclude a processor and memory, for example. The on-board computingsystem 118 can be configured to receive and analyze data from the saidutility sensors and generate images for output by an optional augmentedreality (AR) display device.

The sensor 122 is shown on the extending side-arm 116 of the headmountable device 102; however, the sensor 122 can be positioned on otherparts of the head mountable device 102. For illustrative purposes, onlyone sensor 122 is shown. However, in an example embodiment, the headmountable device 102 can include any number of additional utilitysensors.

Further, although FIG. 1 illustrates two image capture devices 141 and142, more image capture devices can be used, and each can be configuredto capture the same view, or to capture different views. Moreover, thedepicted image capture devices 141 and 142 are primarily tasked withcapturing imaging data required by the polarization analyzer module andany secondary use of these image capture devices as ordinary utilitysensors needs to ensure that the requirements of the polarizationanalyzer are not compromised. Alternatively additional cameras may beinstalled as general purpose image capture devices.

The finger-operable touch pad 124 is shown on the extending side-arm 114of the head mountable device 102. However, the finger-operable touch pad124 can be positioned on other parts of the head mountable device 102.Also, more than one finger-operable touch pad can be present on the headmountable device 102. The finger-operable touch pad 124 can be used by auser to input commands. If more than one finger-operable touch pad ispresent, each finger-operable touch pad can be operated independently,and can provide a different function.

In a further aspect, head mountable device 102 can be configured toreceive user input in various ways, in addition or in the alternative touser input received via finger-operable touch pad 124. For example,on-board computing system 118 can implement a speech-to-text process andutilize a syntax that maps certain spoken commands to certain actions.In addition, head mountable device 102 can include one or moremicrophones via which a wearer's speech can be captured. Configured assuch, head mountable device 102 can be operable to detect spokencommands and carry out various computing functions that correspond tothe spoken commands.

As another example, head mountable device 102 can interpret certain handor eye gestures as user input. As a further example, head mountabledevice 102 can interpret eye movement as user input. In alternativeembodiments, display elements can be introduced to the system. Forexample, the lens elements 110, 112 themselves can include: atransparent or semi-transparent matrix display, such as anelectroluminescent display or a liquid crystal display, one or morewaveguides for delivering an image to the user's eyes, or other opticalelements capable of delivering an in focus near-to-eye image to theuser. Alternatively or additionally, a laser or LED source and scanningsystem could be used to draw a raster display directly onto the retinaof one or more of the user's eyes. Other possibilities exist as well.

F. Example System Architecture

FIG. 10 is a block diagram illustrating an example system architecturefor various embodiments of the present invention. The example systemdepicted comprises a plurality of at least one processor 1005 and memory1010. As depicted by block 1020 a polarization data capture modulecomprises a plurality of image capture devices 1021, a plurality ofpolarization filter devices 1023 and an image capture and polarizingfilter controller 1025. Block 1030 depicts the polarization analyzermodule, which comprises an image matrix mapping module 1031, apolarization optimization module 1033 and a post processing module 1035comprising a smoothing method. The image matrix mapping module 1031 isresponsible for taking images captured by the polarization data capturemodule 1020 and mapping them onto a matrix where each elementcorresponds to an electrically-controllable polarization filter cell 123in a filter grid 110 of a head mountable device 102. The polarizationoptimization module 1033 is responsible for determining a preferredpolarization filter target state for each individual filter cell 123.The post processing module 1035 is tasked with recognizing polarizationpatterns spanning multiple filter cells and applying a smoothingfunction so that undesirable abrupt transitions and single-pixelabnormalities are avoided such as to provide an enhanced userexperience. The polarization filter module is depicted in block 1040 andcomprises a plurality of polarization filter grids 1041 and apolarization filter controller 1043. The polarization filter grids 1041comprise both filter grids 110 and 112 intended for the left and righteye of a user of the embodiment. The polarization filter controller 1040is tasked with converting the polarization targets computed by thepolarization analyzer 1030 and converting the into control inputs forthe polarization filter grid 1040. Block 1050 depicts the user interfacemodule, comprising a polarization selector module 1051 and a pluralityof inter-device communications interfaces 1053. The polarization modeselector can have multiple implementations in a single embodiment, suchas being a tap-pad, a voice command interface or an app on a smartphone.Other implementations are also possible. The inter-device communicationsinterfaces 1053 are used to communicate with user interface componentshosted on devices other than the head-mountable device described invarious embodiments. The said interfaces allow the user to interface asmartphone controller app via a Bluetooth or a wireless local areanetwork (WLAN) connection for example.

G. Example Methods of Operation

The preferred embodiment of the present invention comprises a headmountable device having the general appearance of eyeglasses designedfor sun protection 102. When such device is worn a user 102 has a numberof different possibilities to interact with such device. The primaryobjective of such interaction is generally to select the desired mode ofoperation. The modes of operation for a preferred embodiment aredepicted in FIG. 8. FIG. 2 depicts how the user is able to switchbetween said modes of operation. The preferred method to changepolarizer settings comprises use of the touchpad 240. A tap on thetouchpad causes the selection of a different polarizer mode. The usercan thus iterate through all available modes by means of repeatedlytapping the touchpad. The preferred embodiment also offers the option ofchanging polarizer mode by voice command 250. An advantage of usingvoice commands is that the user can name the desired mode and is notforced to reach the desired mode by means of iteration. A thirdpreferred way of configuring the polarizer is to interface the polarizervia smartphone app 227. For that purpose the head mountable device isinterfaced with a smartphone-type device via a Bluetooth connection 225226. The present invention may also be practiced with other suitablemethods for controlling the user interface of the respective embodiment.

H. Conclusion

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims.

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. In the figures, similar symbols typically identifysimilar components, unless context dictates otherwise.

The example embodiments described herein and in the figures are notmeant to be limiting. Other embodiments can be utilized, and otherchanges can be made, without departing from the spirit or scope of thesubject matter presented herein. It will be readily understood that theaspects of the present disclosure, as generally described herein, andillustrated in the figures, can be arranged, substituted, combined,separated, and designed in a wide variety of different configurations,all of which are explicitly contemplated herein.

With respect to any or all of the diagrams, scenarios, and flow chartsin the figures and as discussed herein, each block and/or communicationcan represent a processing of information and/or a transmission ofinformation in accordance with example embodiments. Alternativeembodiments are included within the scope of these example embodiments.In these alternative embodiments, for example, functions described asblocks, transmissions, communications, requests, responses, and/ormessages can be executed out of order from that shown or discussed,including substantially concurrent or in reverse order, depending on thefunctionality involved. Further, more or fewer blocks and/or functionscan be used with any of the diagrams, scenarios, and flow chartsdiscussed herein, and these diagrams, scenarios, and flow charts can becombined with one another, in part or in whole.

A block that represents a processing of information can correspond tocircuitry that can be configured to perform the specific logicalfunctions of a herein-described method or technique. Alternatively oradditionally, a block that represents a processing of information cancorrespond to a module, a segment, or a portion of program code(including related data). The program code can include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data can be stored on any type of computer readable medium suchas a storage device including a disk or hard drive or other storagemedium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that stores data forshort periods of time like register memory, processor cache, and randomaccess memory (RAM). The computer readable media can also includenon-transitory computer readable media that stores program code and/ordata for longer periods of time, such as secondary or persistent longterm storage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media can also be any other volatile or non-volatile storagesystems. A computer readable medium can be considered a computerreadable storage medium, for example, or a tangible storage device.

Moreover, a block that represents one or more information transmissionscan correspond to information transmissions between software and/orhardware modules in the same physical device. However, other informationtransmissions can be between software modules and/or hardware modules indifferent physical devices.

The particular arrangements shown in the figures should not be viewed aslimiting. It should be understood that other embodiments can includemore or less of each element shown in a given figure. Further, some ofthe illustrated elements can be combined or omitted. Yet further, anexample embodiment can include elements that are not illustrated in thefigures. While various aspects and embodiments have been disclosedherein, other aspects and embodiments will be apparent to those skilledin the art. The various aspects and embodiments disclosed herein are forpurposes of illustration and are not intended to be limiting, with thetrue scope and spirit being indicated by the following claims.

DEFINITIONS AND CLARIFICATIONS

Herein below are a few definitions and clarifications. As used herein:

The terms “a” and “an”, when modifying a noun, do not imply that onlyone of the noun exists.

The term “comprise” (and grammatical variations thereof) shall beconstrued broadly, as if followed by “Without limitation”. If Acomprises B, then A includes B and may include other things.

The term “e. g.” means including without limitation. The fact that an“example” or multiple examples of something are given does not implythat they are the only instances of that thing. An example (or a groupof examples) is merely a non-exhaustive and non-limiting illustration.

In the context of a head mountable device (and components of thedevice), “front” is optically closer to the light source, and “rear” isoptically further from the light source. A stack of polarizationrotators is a display device or a component of a display device; thus, astack of polarization rotators has a “front” and a “rear”.

The term “include” (and grammatical variations thereof) shall beconstrued broadly, as if followed by “Without limitation”.

“Intensity” shall be construed broadly to include any measure of orrelated to intensity, energy or power. For example, the “intensity” oflight includes any of the following measures: irradiance, spectralirradiance, radiant energy, radiant flux, spectral power, radiantintensity, spectral intensity, radiance, spectral radiance, radiantexitance, radiant emittance, spectral radiant exitance, spectral radiantemittance, radiosity, radiant exposure and radiant energy density.

The term “Malus' law” shall be construed broadly to include anyformulation of that law and any computation equivalent to that law.

The term “or” is an inclusive disjunctive. For example “A or B” is trueif A is true, or B is true, or both A or B are true.

“Parallax” includes binocular parallax and motion parallax. A displayexhibits binocular parallax, if the apparent position of an objectviewed by the left eye and the right eye of a human viewer differsbecause of the different positions of the two eyes. A display exhibitsmotion parallax, if the apparent position of an object appears to changeas the viewpoint of the human viewer moves (e.g., by moving the viewer'shead).

A parenthesis is simply to make text easier to read, by indicating agrouping of words. A parenthesis does not mean that the parentheticalmaterial is optional or can be ignored.

To vary something “per pixel” means to vary it at respective pixels. A“pixel” includes the smallest addressable element visible through anexit pupil of an optical device. For example, a light-transmitting headmountable device may have pixels even if it does not comprise a displayscreen.

A “polarization rotator” is a device configured to change thepolarization state of light that travels through the device. Forexample, a polarization rotator may comprise a layer of liquid crystalbetween a pair of transparent electrodes. Or, for example, any devicethat alters the polarization state rotation of light passing through thedevice is a polarization rotator.

The term “polarization state rotation” shall be construed broadly. Forexample, the term includes a rotation of the angle of polarization oflinearly polarized light.

The term “polarizer” means a device that alters light according to thelight's polarization state. For example, a polarizing diffuser is a“polarizer”.

What is claimed is:
 1. A method for adaptive polarization filtering,comprising, in combination: (a) routing incident light through a grid toan entrance pupil of a human eye, wherein said grid comprises aplurality of stacks and wherein each stack comprises a plurality ofelectrically controllable polarization rotators; and (b) using one ormore processors (i) to perform an optimization calculation for glarereduction, wherein the optimization calculation is configured to computea set of polarization rotation targets which are to be induced in theincident light by respective polarization rotators; and (ii) to outputcontrol signals to the respective polarization rotators wherein thecontrol signals relay said polarization rotation targets.
 2. The methodof claim 1, wherein said grid is part of an eyepiece of a see-throughhead-mountable device.
 3. The method of claim 2, wherein the gridcomprises an array of at least 640 by 480 stacks.
 4. The method of claim3, wherein at least one of the plurality of polarization rotatorscomprises silver nanowire-based transparent electrodes.
 5. The method ofclaim 2, wherein the optimization calculation comprises input parametersrelating to pixel-specific sRGB tristimulus values derived from aplurality of polarizer-variant images of a similar field of view as thatseen by the user of the head mountable device.
 6. The method of claim 5,wherein the optimization calculation comprises a plurality oftransformations of the pixel-specific sRGB tristimulus values to CIE xyYcolor space values.
 7. The method of claim 6, wherein the Y-values ofthe CIE xyY color space values are used as parameters for comparingalternative polarizing filter settings in the optimization calculationand wherein the polarization angle of the polarizer associated with thelowest Y-value of a set of polarizer-variant pixel-associated Y-valuesis considered indicative of an optimum polarization rotation target. 8.The method of claim 1, wherein at least one anisotropic absorber ispositioned in the path of the incident light after the plurality of saidstacks.
 9. The method of claim 8, wherein at least one of theanisotropic absorbers comprises a guest-host type liquid crystal cell.10. The method of claim 8, wherein exactly one anisotropic absorber isprovided for the grid.
 11. The method of claim 1 further comprising astep of using the one or more processors to perform a normalizingcalculation relating to a target brightness of light transmitted througheach of the stacks and to output control signals to dynamically controllight transmittance characteristics of the plurality of the stacks.